As material flows through a hollow pipe, a barrel or a tower, the velocity in the central zone is higher, while the velocity in the edge zone is lower, so the residence time distribution of the material in the pipe, the barrel or the tower is quite wide. If the flowing process is accompanied with heat emission or heat absorption, or the material is heated or cooled with jackets, the heat transfer resistance may cause a temperature difference between the central zone and the edge zone. If a chemical reaction occurs, the differences in residence time and temperature may induce nonhomogeneity in composition between the central zone and the edge zone.
The most direct method to overcome these problems is to make material in the central zone and the edge zone in the pipe, barrel or tower to regularly exchange their positions, provided there is no dead space or shortcut, and to do so with low resistance, so as to make an arbitrary particle experience similar radial coordinate change during flowing through the pipe, barrel or tower. When performing a chemical reaction or a mass transfer in a heterogeneous system with a tower apparatus, the two-phase materials involved should remain in counter-current plug flow as long as possible, in order to obtain maximum reaction or mass transferring impetus. Also, the dispersed phase material should be divided into minimum particles, droplets or bubbles, dispersed uniformly in the continuous phase material, in order to provide maximum reaction or mass transferring interface.
To meet the above requirements, there are many plate towers and packed towers with various structural forms in industrial operation at the present time, but their efficiency needs to be improved and operating flexibility needs to be further extended.